snap prevents Disk Devices from being accessed

I wanted to backup the device my /boot partition is mounted on using mozilla. But snap prevents me from doing that.

I use fsck here to illustrate what is happening - clonezilla seems to work when fsck works.

I started by unmounting /boot:

sudo umount /boot/efi sudo umount /bootsudo fsck /dev/sda2  # which is the device for /boot

From that I get the error message

fsck from util-linux 2.37.2e2fsck 1.46.5 (30-Dec-2021)/dev/sda2 is in use.e2fsck: Cannot continue, aborting.

My question is: How can I get fsck to run?

The current workaround is:

• snap disable all installed snaps
• sudo systemctl stop snapd
• reboot

Then everything works.

But there must be a simpler way of accessing /dev/sda2! How can I access it without the interference of snap?